Knife sharpening apparatuses of the type having an abrasive belt and means for supporting and driving the belt along an endless path are well known. It is also well known to use such machines for sharpening knives and other tools having elongated cutting edges. For a knife or the like to be optimally sharpened with such machines the cutting edge must engage the abrasive belt at an appropriate angle and with an appropriate amount of force applied to keep the cutting edge in contact with the belt. During the sharpening procedure heat is generated at and near an area of engagement between the cutting edge of the knife and the abrasive belt. If the applied force is too great, the cutting edge overheats resulting in a change in the microstructure of the cutting edge and a reduction of the surface hardness of the cutting edge. In addition, excessive force applied to the belt by the cutting edge can cause accelerated belt wear. On the other hand, if the applied force is inadequate to keep the cutting edge in contact with the belt, the sharpening procedure may require an undue amount of time. The cutting edge is an intersection of opposing faces of the knife disposed at a predetermined angle from one another. To optimize performance of the cutting edge, the angle between the opposing faces of the knife must be held within close tolerances at the cutting edge. Therefore, angular positioning of the knife relative to the belt affects sharpening quality.
To aid in the proper positioning of and the application of proper force to a knife being sharpened it is known to use a rest having a guide surface inclined with respect to the path of travel of the belt. It is also known that the guide surface includes an index mark established, usually by trial and error, on the surface indicating the point to which a knife is to be moved for proper sharpening. However, this does not preclude the possibility of the knife being accidentally or intentionally moved beyond the index mark, creating overheating of the cutting edge, belt damage and other problems.
U.S. Pat. No. 5,036,626 proposes the use of plastic unloader discs positioned on opposing sides of the belt of an abrading type knife sharpening machine to carry the knife edge away from the belt when excessive force is applied by the user to the knife and belt. However, the unloader discs can wear and therefore become less effective.
Some knife sharpeners of the belt abrading type have belts which travel at a relatively constant speed regardless of the force applied by the knife to the belt during a sharpening operation. In such knife sharpeners, overheating of and damage to the cutting edge can occur quickly when excessive force is applied, because the belt does not slow or stop relative to the force applied.
Belt abrading knife sharpeners have been provided in enclosed housings to protect the user's clothing, fingers or other objects from being entangled with the moving parts of the knife sharpener. However, some housings are comprised of two housing portions rotatably connected by a hinge so that opposing housing portions can be rotated relative to each other to access internal parts of the knife sharpener, for example, for changing the belt. If the two housing portions are rotated apart from one another while the belt is operating, rotating parts thereof are exposed and a safety hazard can result.
Many knife sharpeners are large, heavy and suitable primarily for commercial uses, for example, in a butcher's shop, grocery store or the like. Such knife sharpeners have not been frequently used by individual home owners because the size and weight of the knife sharpener makes it impractical for home countertop use. Moreover, such units generally operate on 120 volt A/C power which requires the knife sharpener to be stationed within access to a suitable power supply and requires use of relatively expensive motors.
Belt grinders or sanders of the general type having a belt drive pulley, at least one driven or idler pulley and an endless abrasive or other belt trained over the pulleys are known in the art, as evidenced by U.S. Pat. Nos. 3,497,336 and 4,294,044. During the operation of such a machine, it is desirable that the belt track is aligned properly over the pulleys. That is, it is desirable that the belt maintain a position substantially laterally centered on the belt engaging faces of the pulleys. However, slight alignment errors in the relation of the axes of the pulleys to one another or slight variations in the lengths of the edges of the belt can cause the belt to move off track by shifting laterally to one side or the other from the desired centered position. In some instances, the belt may run completely off of the pulleys or rub against a wall or other structure of the machine located adjacent one or both of the pulleys or the belt, resulting in the shortening of belt and/or machine life.
To allow for correction of the running path of the belt, it has been common practice in belt abrading machines to provide a means for adjusting the inclination of an idler pulley axis relative to a drive pulley axis. Such adjustment means have however tended to pose various problems of their own, including being of a complex, expensive construction and being difficult to operate or fine tune during operation.
Thus there is a need to provide a knife sharpening machine that accurately sharpens a knife without overheating or damaging the cutting edge, that is light weight, compact, inexpensive, does not require belt alignment and does not pose a safety risk. Prior art methods and systems for addressing these needs are either too expensive, too complicated, ineffective or a combination of all of these. Based on the foregoing, it is the general object of the present invention to improve upon prior art knife sharpening machines and methods and overcome the problems and drawbacks thereof.